Transcript 7 Science Chapter 8 / Microsoft PowerPoint 97

Grade 7 Science
Chapter 8
Solutions… a review
A solution is a homogeneous mixture
ie. they appear as ONE substance
Examples:
tap water
Vinegar
gold jewelry
Making solutions:
solutes and solvents
When you mix two
substances and they form a
solution, you say that one
substance dissolves in the
other substance.
Solutions have 2 parts:
Solute
Solvent
The
The substance
substance that in which the
dissolves
solute dissolves
(found in less (found in the
greatest
amounts)
amounts)
Dissolving...
To mix completely:
the solute dissolves into the
solvent.
Different states of solutes
and solvents
p. 255
 Solvents can be either:
Solid, Liquid, Gas
Solution
Solute
 Solutes can be either:
Solid, Liquid, Gas
Solvent
State of
solute
State of
solvent
Air
Oxygen, carbon dioxide Nitrogen
and other gases
Gas
Gas
Soda water
Carbon dioxide
Water
Gas
Liquid
Vinegar
Acetic acid
Water
Liquid
Liquid
Filtered ocean
water
Sodium chloride (salt)
and other minerals
Water
Solid
Liquid
Brass
Zinc
Copper
Solid
Solid
antifreeze
Alcohol
water
Liquid
Liquid
Can you guess what the
example is?
Hydrogen in
Palladium
Solute
Vinegar
Air
Soda
Filtered sea
water
Brass
Sugar water
Solvent State
Vinegar
Liquid
5% acetic acid
95% water
Liquid
Air
- 78%: Nitrogen
- 22%: oxygen,
carbon dioxide,
other gases
Gas
Gas
Soda
- carbon dioxide
Gas
Liquid
- water
Filtered Sea Water
- Water
Liquid
- Salt and other
minerals
Solid
100 % Brass
- 35g zinc
Solid
- 65% copper
Solid
**Alloy: Solutions made
from two or more metals.
Sugar water
- 1 teaspoon of
Solid
sugar
- 1 cup of water Liquid
In class activity
8-1A: Name that solute and solvent
P.255
p.256
SOLUBLE AND INSOLUBLE
Soluble
https://www.youtube.com/watch?
v=khgOTDvG-4A
If the particles of the solute are
more attracted to the particles of
the solvent.
Dissolving occurs.
The solute is said to be soluble
in that solvent.
(ie. Solution)
Insoluble
If the particles of the solute are
more attracted to their own
particles than the solvent particles.
Dissolving does NOT occur.
The solute is said to be
insoluble in that solvent.
(ie. Mechanical)
Soluble or Insoluble?
soluble
insoluble
Insoluble in some solvents,
soluble in others
p.257
Why some substances dissolve
p.258
1. Solute becomes attracted to the solvent.
 Solute particles are attracted to solvent
particles - so they mix.
 Example: sugar particles are attracted to the water
particles, mixing with the water particles.
2. Movement
 Mixing causes movement. When 2 substances
are mixed, the weak attractions are broken by
the motion of the particles.
 Example: oil is mixed with gasoline. Both have very
weak attractions that are broken by the motion.
Why some substances do
not dissolve
 Solute is NOT attracted to the
solvent.
 For fat particles to dissolve in
water, the milk fat particles
would have to be more attracted
to the water particles.
 Fat particles are not more attracted
to the water particles.
 Fat particles stay together and form
insoluble globules in the liquid
Milk
In class activity
Reading check p.257 & 258
Check your understanding p. 261
8.2
Page 262
CONCENTRATION AND
SOLUBILITY
Concentration and
solubility
Compare the two
cups of tea…
Concentrated solution
Darker tea
Large mass of dissolved
solute for a certain
quantity of solvent.
Dilute solution
Lighter tea
Small mass of dissolved
solute for a certain
quantity of solvent
Concentration is…
The quantity of solute that
is dissolved in a certain
quantity of the solvent.
Can be described
qualitatively or
quantitatively.
Quantitative
Qualitative
Using
Using words
numbers.
such as like
This is
“dilute” or
“concentrated” especially
important
when safety is
an issue!
Student Practice… (page 471)
Qualitative or Quantitative?
#1(a). Food coloring made the water blue.
Qualitative
 (b). Adding 3 mL of food coloring turned
250 mL of water blue.
Quantitative
#2(a). The water became warmer.
Qualitative
 (b).
The water’s temperature increased
by 5 degree Celsius.
Quantitative
#3(a). We needed just over a dozen floor
tiles for our model room.
Qualitative
 (b). We needed 14 floor tiles for our
model room.
Quantitative
#4(a). The liquid boiled in 5 min.
Quantitative
 (b). The liquid took only a few minutes
to boil.
Qualitative
#5(a). The mass of this solid is 5g more
than that one.
Quantitative
 (b). This solid is heavier than that one.
Qualitative
6(a).
He drinks eight glasses of water each
day.
Qualitative
 (b). He drinks 2L of water each day.
Quantitative
A limit to concentration
p.264
Make a salt solution:
Add a spoonful… dissolved!
Add a second spoonful…
dissolved!
Add a third, fourth and
more… It becomes more
concentrated!
Eventually you reach a
point where salt will NOT
dissolve any more.
Notice the lump of
undissolved solid that
is left on the spoon
Saturated vs. Unsaturated
Saturated
Will form when no
more solute will
dissolve at a certain
temperature
Unsaturated
More solute is able to
dissolve at a certain
temperature
Concentration is…
 Expressed as the amount of solute
per unit volume.
 Examples:-g/L or g/mL
-ppm (parts per million)
- percentage be mass
Which is dilute and which is more
concentrated for each example?
 Example 1:
Orange juice from concentrate: ___________
Weak Kool-Aid: ____________________
 Example 2:
A solution with a concentration: 20g/100mL _______
A solution with a concentration: 25g/25mL_________
 Example 3:
A solution with a concentration: 20/80mL__________
A solution with a concentration: 20/100mL ________
Time to think…
Concentrated solutions can be:
1. Adding more solute and keeping the
amount of solvent the same.
2. Keeping the amount of solute the
same and reducing the amount of
solvent.
Example
 boiling off the water while making jam
a solution could be considered
“concentrated” and still be unsaturated.
In class activity
Rate of dissolving
p.265
The rate of dissolving refers to how
quickly a solute dissolves in a solvent.
Factors that affect the rate of
dissolving include:
1. Stirring
2. Temperature
3. Size of solute
4. Pressure
1. Stirring
A solute will dissolve more quickly if you
stir it.
Example: fruit drink with drink crystals.
Stir the mixture to increase the rate of
dissolving.
Stirring: PTM
p.265
A: Before mixture is stirred.
 Movement depends on the natural
movement of the nearby water
particles.
 The solution close to the crystal is
more concentrated and the solution
farther from the crystal is more dilute.
B: While stirring mixture
 The solute and solvent interact more
quickly.
 The concentrated solution is pushed
away from the crystal at the same
time it pushes dilute solution closer to
the crystal.
2. Temperature - SOLID
As temperature increases:
 The faster the solute will
dissolve.
Temperature - GAS
As temperature increases:
 The solubility of a gas
generally decreases.
It will taste: “flat” - warm
pop if left open for a
period of time
http://www.youtube.com/watch?v=K3j9
HAsoV5Q
3. Size of solute
Smaller pieces of solute will
dissolve more quickly than
larger pieces.
Dissolving a solid in a liquid
takes place at the surface of the
solid.
Breaking a large solid into
smaller pieces, expose more
surfaces - creating a larger
surface for the solvent to interact
with.
3. Pressure
page 267
Gases are
more soluble
in liquids
under higher
pressure.
Pressure:
Open a bottle or can of pop!
As pressure increases, the solubility of a gas
generally increases.
Higher pressure forces extra gas particles into
the spaces between the water particles.
As pressure decreases, the solubility of a gas
generally decreases.
Open the can and the pressure inside lowers
quickly. Gas solute comes out of the solution. IE:
bubbles
CORE LABORATORY
ACTIVITY: HOW DOES
TEMPERATURE AFFECT
SOLUBILITY?
In class activity